Maik Zimmermann

Fabrication and characterization of linear diffusers based on concave micro lens arrays

We present a new approach of beam homogenizing elements based on a statistical array of concave cylindrical microlens arrays. Those elements are used to diffuse light in only one direction and can be employed together with flys eye condensers to generate a uniform flat top line for high power coherent light sources. Conception, fabrication and characterization for such 1D diffusers are presented in this paper.

Microlens laser beam homogenizer: from theory to application

Many applications in laser manufacturing like semiconductor lithography, micro-machining, micro-structuring or material-analysis require a homogeneous intensity distribution of the laser beam over its complete profile. Refractive and diffractive beam homogenizer solutions have been developed for this challenge, but their applicability strongly depends on the physics of the individual laser beam. This paper investigates the influence of laser beam properties like spatial coherence for microlens beam homogenizers. Diffraction at the small lens apertures and interference effects of periodic arrays are explained by using diffraction theory. Different microlens beam homogenizer configurations are presented. Design considerations that might be helpful for the layout of a specific microlens beam homogenizer system are discussed. It is shown that, among other factors, the Fresnel number is the most important quantity to characterize the influence of diffraction effects on microlens laser beam homogenizers. The influence of the spatial partial coherence will be explained for the example of a Flys eye condenser. For cw laser sources, the influence of a rotating diffuser plate on grating interference and speckles effects is investigated. Finally, the theory will be compared to some practical examples in planar laser measurement techniques, in combustion diagnostics and micromachining with Excimer lasers.

Multifunctional Micro-Optical Elements for Laser Beam Homogenizing and Beam Shaping

Refractive, diffractive and reflective micro-optical elements for laser beam shaping and homogenizing have been manufactured and tested. The presented multifunctional optical elements are used for shaping arbitrary laser beam profiles into a variety of geometries like, a homogeneous spot array or line pattern, a laser light sheet or flat-top intensity profiles. The resulting profiles are strongly influenced by the beam properties of the laser and by diffraction and interference effects at the micro-optical elements. We present general design rules for beam shaping and homogenizing. We demonstrate the application of such multifunctional micro-optical elements for a variety of applications from micro-laser machining to laser diagnostic systems.

Laser micro adjustment—from new basic process knowledge to the application

Laser micro bending and its controlled variant, laser micro adjustment, have been known for many years. Different theories on the working principle, mainly differing in interaction time and energy flux density, have been evolved and experimentally proven. The temperature gradient mechanism and the buckling mechanism are the most established laser adjustment techniques. However, as interaction times are getting shorter with the development of new laser sources, additional phenomena are being detected and new interaction principles have to be investigated. In this paper the use of the thermal upsetting mechanism for adjusting fiber optical components will be demonstrated. An actuator for micro positioning of optical fibers relative to collimating optics is designed using numerical simulations and experimental results. The benefit of laser adjustable actuators in building an automated, modular production line will then be presented by introducing a system developed for the assembly of fiber optical component...

Flexible beam shaping system using fly’s eye condenser

Normally, flys eye condensers are used to homogenize light. However, in the case of fully coherent light, a flys eye condenser, in connection with some simple optical elements, such as a diffractive axicon, a grating, and a telescope, can be used as a quite flexible beam shaping system, forming arrays of rings, parts of rings, or other structures with varying diameters. We present the principle, some simulation results, and some first experimental results.

Combination of a micro-lens multi-spot generator with a galvanometer scanner for flexible parallel micromachining of silicon

Multi focus optics are used for parallelizing production and for large-scale material processing. These elements split the beam into a periodic spot pattern with a defined grid and spot size. The challenge lies in the generation of a homogeneous envelope. Additionally the demand for flexible systems for an in-process changing of optical properties increases. Different components for multi spot generation like diffractive optical elements or micro lens arrays have been investigated. Diffractive optical elements offer large degree of freedom in the generation of arbitrary intensity distributions. In the paper we demonstrate the use of a diffractive element in combination with a multi spot generator. Within the paper we present the investigation of a micro lens array in a flys eye condenser setup for the generation of homogeneous spot patterns. The multi spot generator is combined with a galvanometer scanner for forming an arbitrary shaped laser beam into a spot-, ring or arbitrary array pattern. We show the principal functionality of the multi-spot generator. Furthermore constrains of this setup are demonstrated. The multi spot scanner is used for micro structuring of silicon with a nanosecond diode pumped solid state laser. The ablation rate and structure quality are compared to single spot processing.

Beam Guidance, Focal Position Shifting and Beam Profile Shaping in Ultrashort Pulsed Laser Materials Processing

In ultrashort pulsed (USP) laser micro-processing several optical and optomechanical components are needed to enable the desired process. Besides the USP laser itself, systems to guide and focus the laser beam are mandatory in almost all applications. Furthermore beam profile shaping , e.g. the creation of top-hat or super-Gaussian beam profiles, results in beneficial effects for many applications, such as increased efficiency and superior quality. In this chapter an overview of both established and up-to-date technologies regarding beam guiding , focal position shifting and beam profile shaping will be presented. For beam guidance and focal position shifting comparable key parameters will be stated to enable easy comparability. As an outlook on probable future applications, both temporal and spatial polarization profile shaping will be presented.

Investigation of micro lens multi spot generator for parallel micromachining of silicon with picosecond and nanosecond laser

Multi spot optics are used for parallelizing production and therefore enabling large-scale material processing. These elements split the beam into a periodic spot pattern with a defined grid and spot size. The challenge lies in the generation of a homogeneous envelope. Micro lens arrays offer a high flexibility in dimensions and shapes for the generation of different multi spot patterns. Within the paper we present the investigation of a micro lens array in a flys eye condenser setup for the generation of homogeneous spot patterns. The principal functionality of the multi spot generator is shown and constraints of this setup are demonstrated. The multi spot generator is used for micro structuring of silicon with a nanosecond and a picosecond laser both at a wavelength of 355 nm. The multi spot generator splits the incoming beam into a linear spot matrix with 28 single spots. The ablation rate and structure quality using a multi spot generator are investigated compared to conventional treatment. It can be shown, that both ablation efficiency and structure quality can be increased by using a multi spot generator.

Photonics in medicine – From diagnostics to training

Medical photonic technologies already address a wide range of human applications. With the advancing knowledge about optics more and more possible applications arise. Here we will present three different novel examples ranging from diagnostic analyses to perceptual training of sportsmen that all use new photonic knowledge.To predict diseases such as laryngitis (inflammation of the larynx) via non-contact and minimal invasive measurements we develop an optical system that allows the analysis of the 3-dimensional vocal dynamics by using a high-speed camera and associated software. With a triangulation based sensor and 200 laser generated measuring points the 3D surface can be calculated.For detection of cancer or other pathological lesions in the stomach we implement a hyperspectral reflectance and multispectral fluorescence video endoscope. It is currently tested with hard tissue phantoms. Further studies like ex-vivo and in-vivo animal experiments are planned. The final goal is to develop reliable and robust hardware and software to automatically distinguish between cancerous and normal tissue.In sports applications but also in other areas higher performance of depth vision results in lower reaction times and higher precision. Literature proves that vision can be improved by perceptual training. We develop a virtual training system for depth vision of sportsman. As a first step the performance of depth vision is evaluated by an interactive gesture controlled vision test that simulates depth by stereo rendering.These examples show that photonics in medicine helps to better understand human body and thus produces new fields of application in diagnostics and therapy.Medical photonic technologies already address a wide range of human applications. With the advancing knowledge about optics more and more possible applications arise. Here we will present three different novel examples ranging from diagnostic analyses to perceptual training of sportsmen that all use new photonic knowledge.To predict diseases such as laryngitis (inflammation of the larynx) via non-contact and minimal invasive measurements we develop an optical system that allows the analysis of the 3-dimensional vocal dynamics by using a high-speed camera and associated software. With a triangulation based sensor and 200 laser generated measuring points the 3D surface can be calculated.For detection of cancer or other pathological lesions in the stomach we implement a hyperspectral reflectance and multispectral fluorescence video endoscope. It is currently tested with hard tissue phantoms. Further studies like ex-vivo and in-vivo animal experiments are planned. The final goal is to develop reliable and rob...

Dynamic array spot shaping for laser micro machining

Laser manufacturing of microstructures using a single focus is a well known technology. Multi-spot optics are applied for process parallelizing if the demand on throughput in mass production rises or large areas of material have to be processed. Diffractive optical elements (DOEs) are used for parallel laser processing of a repetitive structure. These elements split the beam into a periodic spot pattern, where each spot shows the same shape and energy. This allows simultaneous manufacturing of several equal shaped structures at the same time. For patterning a surface this is state of the art and the appropriate technique to reduce processing time while maintaining a high lateral resolution as well as a good relative positioning of the structure due to the DOE. We investigate the usage of microlens arrays as multifunctional elements for forming an arbitrary shaped laser beam into a spot-, a ring-spot- or a line-array pattern. It can be shown that the intensity distribution of each spot is equal to the intensity distribution of all other spots in the whole pattern. The shape of the spots is defined by the angular distribution of the incident beam. We demonstrate that besides other optical properties the output beam profile strongly depends on the Fresnel-Number and is influenced by diffraction and interference effects. We present important design rules which consider geometrical and physical optics. The properties of the spot arrays, like spot diameter, Rayleigh length and beam divergence in dependency of beam and system properties are investigated. Finally we will show some laser micro structuring and micro drilling results in different materials.